1. Field of the Invention
The invention relates to a selection device for delivering a gas emanating from one of two feed lines to an apparatus, especially a trace-impurity analyzer such as an atmospheric-pressure ionization mass spectrometer.
2. Description of Related Art
Such a selection device, designed to feed a trace-impurity analyzer either with a gas to be analyzed or with a "calibration" gas which is a pure gas or one containing impurities at precisely known concentrations, is known from Document FR-A-2714968, owned by the assignee of the present invention. The device of the aforementioned document comprises a first and a second line which feed respectively an analysis gas and a calibration gas. Each feed line emerges in a respective purge line. The feed lines for the two gases are connected to the analyzer via a line which connects the two feed lines and via a common line for delivering gas to the analyzer.
The parameters relating to introduction of the gas into the analyzer are controlled, on the one hand, using an upstream pressure regulator mounted on a discharge line connected as a bypass to the common delivery line and, on the other hand, using a flow regulator mounted on an additional purge line connected to an outlet of the apparatus.
Each purge line of the feed lines includes a mass flowmeter. These flowmeters allow selection either of the gas to be analyzed or the calibration gas. It may therefore be understood that for selecting the gas delivered to the analyzer or for controlling the parameters relating to the introduction of the gas into the analyzer, use is made of three mass flowmeters, placed in each of the purge lines, as well as an upstream pressure regulator placed in a line branched off from the common line for delivering gas to the apparatus.
The present invention aims to simplify the known device by providing a selection device which is simpler and more economic.